Variable ratio blood-additive solution device and delivery system

ABSTRACT

A method and apparatus for delivering on command any ratio of blood to blood-additive solution of a blood/solution mixture during cardio vascular and cardiac perfusion procedures and more particularly to intermittently and/or continuously delivering on command any ratio of blood to cardioplegia solution of a blood/cardioplegia mixture during cardiac surgery.

BACKGROUND OF THE INVENTION

This is a Continuation Application of U.S. application, Ser. No.08/026,277 filed Mar. 4, 1993 now U.S. Pat. No. 5,322,500.

FIELD OF THE INVENTION

The present invention relates to a device and system for delivering oncommand any ratio of blood to blood-additive solution of ablood/solution mixture during cardio vascular and cardiac perfusionprocedures and more particularly to intermittently and/or continuouslydelivering on command any ratio of blood to cardioplegia solution of ablood/cardioplegia mixture during cardiac or "open heart" surgery.

Generally, cardioplegia is used in conjunction with hypothermia. Thistechnique is commonly called cold cardioplegia. Based on the preferenceof the cardiac surgical team, a crystalloid chemical solution or somemixture of the solution and blood mixture is intermittently orcontinuously perfused to arrest the heart. For example, using coldcardioplegia, the heart is reperfused approximately every twenty minutesto keep the heart arrested.

Recently, open heart surgeons are utilizing a new technique called warmcontinuous blood cardioplegia. This technique does not use hypothermia,rather, it continually uses a cardioplegia mixture of warm(approximately 37 degrees centigrade) oxygenated blood and solutionmixture throughout the cardiac surgery. See the Perfusionist'sPerspective of Warm Continuous Blood Cardioplegia: A New Technique ofMyocardial Protection, A. Karim Jabr, C.P., and Antony Panos, M.D.,Proceeding of the American Academy of Cardiovascular Perfusion, Vol. 10,August 1989. This article is hereby incorporated herein by reference asthough fully set forth herein. This technique appears to be safe andeffective in prolonging high risk procedures, prolonging operative time,substantially eliminating the period of ischemia, limiting the periodand injury of reperfusion, attaining exceptional myocardialpreservation, and abolishing the detrimental effects of hypothermia.

Generically, these methods fall under the general category of myocardialprotection techniques. Whether the blood cardioplegia is warm or coldblood, or intermittently and continuous, the blood and solution mixtureis predetermined, typically in a 4 to 1 ratio, blood to solution.Presently, the ratio of blood to solution is pre-operatively fixed bythe diameter of the tubing transferring the blood (typically 1/4 inchdiameter tubing) and the solution (typically 1/16 or 1/8 inch diametertubing). Thus, the ratio is fixed throughout the operation. This mannerof delivering the blood and solution cans cause certain complicationsduring the operation. In addition, the fixed ratio may cause certaincomplications on a patient by patient basis, during the operation.

For instance, simultaneously using tubings of different diameter in thesame pump head can unfortunately cause bunching of the tubing orinappropriate occlusion of both the 1/4-inch and the 1/16-inch line.Obviously, bunching of the tubing could lead to adverse consequences forthe patient as a result of the time that it takes the perfusionist orphysician to correct the problem. In addition, changing the bunchedtubing during the operation increases the chance of line contaminationor air getting into the system. Hence, a single tube is desirable.

Further, the typically used ratios of blood to solution, e.g. 4:1 and2:1, that are pre-operatively fixed, may not necessarily be the optimalratio for the patient, either when initially perfusing the heart orreperfusing the heart to keep it arrested during the operation. Inaddition, delivery of fixed ratio of blood/solution mixture with warmcardioplegia, the heart is continually perfused with solution that ismostly composed of water, causing tissue cells to swell. When the heartis revived, non-blood fluids in the tissue or lungs cause the heart towork harder, thereby straining the heart and prolonging recovery.Moreover, some heart surgery teams do not use a blood/solution mixturerather they perfuse the heart with pure solution. Whatever thepreference may be, increasing the solution delivered to the heart usingthe present systems, increases the total volume of fluid delivered tothe heart and correspondingly varies the pressure on the aortic valve.Variation of the pressure on the aortic valve may affect the competencyof the valve and may cause distension. Thus, it is desirable to controlthe amount of solution and/or vary the blood/solution ratio to customizethe blood/solution mixture for each patient and to adjust this ratioduring the operation or, if preferred, to intermittently deliver puresolution as necessary.

It would be highly advantageous therefore, to remedy the foregoing andother deficiencies and inherent limitations associated with the deliveryof a blood/blood-additive solution mixture of a pre-determined ratioduring cardio vascular and cardiac perfusion procedures.

Accordingly, it is a principal object of the device and system of thepresent invention to provide a device and system to selectively vary theratio of blood to blood-additive solution from either all blood to puresolution and any ratio of the two, either continuously orintermittently, throughout the cardio vascular and cardiac perfusionprocedure or surgery.

It is an object of the device and system of the present invention toprovide a device and system that requires a single tube blood-additivesolution pumping arrangement to deliver the blood and/or solution to theperfusion site.

It is a further object of the device and system of the present inventionto vary the ratio of blood to solution without changing the total volumeand maintaining a consistent pump flow rate and aortic pressure.

It is an advantage of device and system of the present invention to beutilized in either warm or cold cardioplegia.

It is a further advantage of the device and system of the presentinvention to permit the perfusionist to use either a single tube ordouble tube, blood-additive solution pumping arrangement.

It is a further advantage of the device and system of the presentinvention to permit the perfusionist to use the device and system forall types of adult and pediatric cardiac surgery, including, coronaryartery bypass surgery, valvular surgery, and other vascular valvesurgery requiring cardioplegia.

It is a further advantage of the device and system of the presentinvention to minimize the delivery of excess solution whereby lesswater, or other non-blood fluids, is absorbed by the tissues and lungs,reducing post-operative heart strain, thereby shortening the recoveryperiod.

The foregoing and more specific objects, advantages and features of thepresent invention will become readily apparent to those skilled in theart from the following detailed description of the preferred embodimentthereof taken in conjunction with the drawings.

BRIEF SUMMARY OF THE INVENTION

The device in the system of the present invention vary the ratio ofblood to blood-additive solution of a blood/solution mixture from eitherall blood to pure solution in any ratio of the two, either continuouslyor intermittently. The device of the present invention comprises asolution conduit and a mixing coupler having a solution inlet, a bloodinlet and a blood/solution mixture outlet. The solution conduit isconnected to the solution inlet and the blood conduit is connected tothe blood inlet. A blood/solution conduit is connected to theblood/solution outlet. The blood/solution conduit has an outlet adaptedto connect to a site of perfusion. A fluid regulating means forselectively controlling the flow of solution, such as a valve, is in thesolution conduit. The device invention may further comprise, a one-wayvalve, located between the regulating means and the solution inlet, thatprohibits fluid flow from the solution inlet. The device invention mayfurther comprise a second fluid regulating means for selectivelycontrolling or stopping the flow of blood, located in the blood conduit,and instead of or in addition to the solution regulating means. Thedevice invention may further comprise a means for continuously andinstantaneously monitoring and displaying the ratio of blood to solutionof the blood/solution mixture. The monitoring and displaying meanscomprise a plurality of fluid flow measuring means in at least two ofthe blood conduit, solution conduit or blood/solution conduit, and acomputer to calculate the ratio of blood to solution based upon themeasurements from at least two fluid flow measuring means. Each fluidflow measuring means are adapted to provide an electronic signalcorresponding to the instantaneous fluid flow. In an alternativeembodiment of the device invention, the monitoring and displaying meanscomprise two pressure measuring means and a means for measuring theinstantaneous volume of blood/solution mixture delivered to theperfusion site. In the alternative embodiment, one pressure measuringmeans is located at the source of the solution and the other pressuremeasuring means is located near the connection of the solution conduitand solution inlet. The computer means calculates the ratio of blood tosolution based upon the measurements of the pressure measuring means,the known density of the blood-additive solution, the distance betweenthe points of measurement, the area of the solution conduit, and themeasured instantaneous volume of blood/solution delivered to the site ofperfusion.

The system invention comprises either aforementioned device invention, aplurality of solution sources connected to the device invention, anoxygenated blood source connected to the device invention, a blood pumpdrawing the oxygenated blood from the source to the device invention,and a blood/solution pump drawing the blood/solution mixture from thedevice invention, and a blood/solution pump drawing the blood/solutionmixture from the device to the site of the perfusion. For the systeminvention comprising the alternative device invention, theblood/solution pump is retrofitted with the blood/solution volumemeasuring means which comprises an angular rotation sensing means andangular rotation indicators on the pump head of the blood/solution pump.The blood/solution volume measuring means is adapted to provide anelectronic signal corresponding to the angular distance traveled by thepump head to the monitor and displaying means. The computer meanscalculates the instantaneous blood/solution volume delivered based uponthe measurement of the blood/solution volume measuring means and theknown volume delivered by the pump at a known rotation rate of the pumphead. As previously described, the computer means calculates the ratioof the blood to solution of the blood/solution mixture delivered to theperfusion site.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawings accompanying the disclosure and the various views thereof maybe briefly described as:

FIG. 1 is a generalized view of the device invention.

FIG. 2 is a generalized view of the system invention.

FIG. 3 is a more detailed view of a portion of an alternative embodimentof the device invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The variable ratio, blood-additive solution, mixing device 10 of thepresent invention is shown generally in FIG. 1. The device 10 comprisesa solution conduit 40 through which a blood-additive solution, such ascardioplegia or potassium solution, flows. The solution conduit 40having an inlet 41 connected to a source selecting means 60 forselecting one solution source from a plurality of solution sources, suchas solution sources 70 and 72. The selecting means 60 has a plurality ofinlets, one for each solution source. Each solution source is connectedto the selecting means 60 by a solution source conduit. In FIG. 1,solution conduit 52 connects the selecting means 60 to solution source70 and solution conduit 54 and connects selecting means 60 to a solutionsource 72. In an alternative embodiment of the device invention, theselecting means 60 is a three-way valve that is adapted such that itssetting is read by a sensor 64. The sensor 64 conveys the position ofthe selecting means 60, i.e. which source is providing the solutionflow, by means of an electronic signal to the computer 80.

The outlet of the solution conduit 40 is connected to a variable valve20. The variable valve regulates and controls the rate of flow ofsolution. A further solution conduit 42 connects the outlet of thevariable valve 20 to the inlet of a one-way valve 24. The purpose of theone-way valve 24 is discussed below. Generally, the one-way valve 24permits the flow of solution in one direction and prohibits the flow ofany fluid, e.g. solution, blood, or blood/solution mixture, from backingup into the solution sources.

A blood conduit 30 has an inlet 31 connected to a source of blood,preferably oxygenated blood. The outlet of the blood conduit 30 isconnected to a butterfly valve 26. In the preferred embodiment, thebutterfly valve 26 either permits the full flow of blood or stops theflow of blood. In an alternative embodiment of the device invention, thebutterfly valve 26 can be used to regulate the flow of blood like thevariable valve 20 regulates the flow of solution. In the alternativeembodiment, the butterfly valve 26 can be used instead of the variablevalve 20 or in addition to it.

FIG. 1 also shows a Y-connector 21 having a blood inlet 22, a solutioninlet 22' and a blood/solution mixture outlet 23. The blood inlet 22 isconnected to the outlet of the butterfly valve 26 by a blood conduit 32.The solution inlet 22' is connected to the outlet of the one-way valve24 by a solution conduit 44. As indicated in FIG. 1, the solution flowsunder force of gravity from the source, 70 (or 72), through the solutionconduits 52 (or 54) and 40, the variable valve 20, the solution conduit42, the one-way valve 24, and solution conduit 44. The flow of solutionthen enters the solution inlet 22' of the Y-connector 21 and the flow ofblood enters the blood inlet 22, thereby causing the solution and bloodto mix in the Y-connector 21 and exit the Y-Connector 21 through itsblood/solution mixture outlet 23. The outlet 23 is connected to ablood/solution mixture conduit 34. The outlet 35 of the conduit 34 isadapted to direct the blood/solution mixture to the site of perfusion,i.e. the coronary arteries of a patient's heart undergoing cardiacsurgery. The site of perfusion, however, may also be another organ ormember of a patient's body, not necessarily undergoing a surgicaloperation, or an experimental site in a controlled laboratory setting.

In the preferred embodiment of the device invention 10, as shown in FIG.1, the variable valve 20 in regulating the flow of solution alsoregulates the ratio of blood to solution in the blood/solution mixture.A physician or perfusionist can thus continuously or intermittentlyselect any desired ratio of blood to solution and selectively vary theratio on command during the course of perfusion, or more particularly atany time during a cardiac surgery. The device invention of the preferredembodiment can be utilized with either cold or warm cardioplegia and canbe utilized in any cardiovascular surgery that includes perfusion,especially perfusion of a blood-additive solution, such as cardioplegia.Further, a physician may deliver pure crystalloid to the perfusion siteby turning the butterfly valve 26 to the off position, thereby stoppingthe flow of blood. The physician may also direct pure oxygenated bloodto the perfused site by turning the variable valve completely off,thereby stopping the flow of solution into the Y-connector 21.

FIG. 1 further shows means for continuously monitoring the ratio ofblood to solution of the blood/solution mixture. At least two of theblood flow measuring means 12, the solution flow measuring means 16, andthe blood/solution mixture flow means 14 are used to continuouslymeasure the instantaneous flow rate or volume delivered of blood,solution, and blood/solution mixture, respectively. Each of theaforementioned means are in-line measuring means, that is, each measuresthe fluid flow in the respective fluid conduit.

Generally, the flow measuring means may be placed anywhere along thefluid conduit. With respect to blood flow measuring means 12, it couldbe placed generally between the inlet of the blood conduit 30 and theoutlet of blood conduit 32. Regarding the solution flow measuring means16, it could be located between the inlet of solution conduit 40 and theoutlet of solution conduit 44. Concerning the blood/solution mixtureflow measuring means 14, it could be located between the inlet andoutlet of blood/solution mixture conduit 34. As will be described withrespect to the variable ratio blood-additive solution delivery system ofthe present invention, placement of the flow measuring means will befurther specified.

Each flow measuring means 12, 14, and 16 are adapted to provide anelectronic signal corresponding to the rate of flow of the fluid.Further, each flow measuring means is electronically connected to thevariable ratio cardioplegia device (VRCD) computer 80. The VRCD computer80 is programmed such that it calculates the ratio of blood to solutionof the blood/solution mixture. At least two different flow measurementsare necessary in order to determine the ratio. All three of the flowmeasuring means are not necessary and variations of the preferredembodiment may include flow measurements from any permutation of theflow measuring means 12, 14 and 16. In order to calculate the ratio,however, the solution flow rate and blood flow rate, or the solutionflow rate and blood/mixture flow rate, or the blood flow rate andblood/solution flow rate, must be measured. For example, if the solutionflow rate and blood flow rate are measured, the ratio is the blood flowrate divided by the solution flow rate. If the solution flow rate andblood mixture flow rate are measured, the ratio is the differencebetween the blood/solution mixture flow rate and the solution flow ratedivided by the solution flow rate. And if the blood flow rate andblood/solution mixture flow rate are measured, the ratio is the bloodflow rate divided by the difference between the solution/blood mixtureflow rate and the solution flow rate.

As will be described below, the VRCD computer 80 may further comprise ameans to display the ratio of blood to solution and the flow rate orvolume delivered of blood, solution and blood/solution mixture. Sincethe flow rate measuring means 12, 14 and 16 continuously measure theinstantaneous flow of blood, solution, blood/solution mixture,respectively, and are electronically connected to the computer 80 havinga display, the physician or perfusionist can monitor the ratio andselect a desired ratio by manipulating the variable valve 20 (and/or thebutterfly valve 26) and reading the ratio from the computer display. Analternative preferred embodiment of the device invention 10' utilizespressure measuring means 18 and 16' instead of flow measuring means 12,14 and 16. This embodiment will be further discussed in the followingdetailed description of the variable ratio, blood-additive solutiondelivery system.

The variable ratio, blood-additive solution delivery system 100 of thepresent invention is shown generally in FIG. 2. The system 100 comprisesa plurality of blood-additive solution sources, e.g. 70 and 72, such ascardioplegia. The system invention further comprises the device 10'. Thedevice 10' is connected to the solution sources 70 and 72 by solutionconduits 52 and 54 respectively. The black box 66 includes the firstpressure measuring means 18, the source selecting means 60, the pressureselecting means 62 and the source selecting means sensor 64, shown inFIG. 1. The pressure measuring means 18 is inline with the solutionconduits 52 and 54 via pressure sensor means 53 and 53', respectivelyThe pressure selecting means 62 selects the solution source whosepressure is being measured by the first pressure means 18. The firstpressure measuring means 18 is adapted to provide an electronic signalcorresponding to the solution pressure to the VRCD computer 80.

The device 10' further comprises an acceleration manifold 40' connectingthe outlet of source switching means 60 to the input of variable valve20. The acceleration manifold 40' is a conduit for the flow of solutionflowing under the force of gravity from the solution source to thevariable valve 20. Near the connection of the acceleration manifold 40'and the variable valve 20 is a second pressure measuring means 16' thatis in-line with the acceleration manifold 40'. This second pressuremeasuring means is also adapted to provide an electronic signalcorresponding to the pressure at that point to the VRCD computer 80. Therectangular box 19 includes the blood conduit 30, the blood conduits 30and 32, the butterfly valve 26, the Y-connector 21, the solutionconduits 42 and 44, the variable valve 20, the oneway valve 24 and theinlet portion of blood/solution mixture conduit 34. The rectangular box19 also has variable valve control knob 20' and butterfly control knob26'.

As further shown in FIG. 2, the blood/solution mixture conduit 34extends through a blood/solution mixture pump 86. The pump 86 draws theblood/solution mixture from the outlet of the Y-connector 21 through theblood/solution conduit 34 to the coronary arteries of the patient'sheart. Pump 86 is adapted or retrofitted with a rotation sensing means98 for determining the angular distance traveled by the rotating pumphead 87. The rotation sensing means 98 can be an optical code reader ora electromagnetic detector. The encoder markings 99 on the pump head 87can correspondingly be either optical indicators or metal or magneticcontacts. The more discreet the rotational indicators 99, the moreaccurate the rotational sensor will be able to determine the angulardistance traveled by the pump head 87. The rotation sensing means 98 isadapted to provide an electronic signal corresponding to the angulardistance to the VRCD computer 80. Using the manufacturer'sspecifications that set forth the volume output of the pump 86 at aparticular pump head rotation rate, the VRCD computer 80 can beprogrammed to calculate the instantaneous flow rate-of theblood/solution mixture leaving the pump 86 through the conduit 34.

As further shown in FIG. 2, the system invention of the preferredembodiment further comprises a split connector 90 having an inlet 91, afirst outlet 92 and a second outlet 93. The second outlet 93 isconnected to the inlet of the blood conduit 30. The outlet 91 isconnected to a blood conduit 29 connected to a blood oxygenator 82. Theblood conduit 29 runs from the oxygenator 82 through a blood pump 84.The pump 84 draws the oxygenated blood from the oxygenator 82 and drivesthe oxygenated blood through the blood conduit 29 to the split connector90 where a portion of the oxygenated blood is delivered via the bloodconduit 30 to the device invention 10'. Another portion of theoxygenated blood is sent to the aorta of the patient's heart through ablood conduit 31 having an inlet connected to the outlet 92 and anoutlet adapted to deliver blood to the aorta.

The VRCD computer 80 has inputs to accept the electronic signals fromthe first pressure measuring means 18, the second pressure measuringmeans 16' and the rotational sensor 98. The computer 80 is programmed tocalculate the instantaneous solution volume delivered by using themeasured pressures at the solution source 70 or 72 and near the bottomof the acceleration manifold 40', according to the Bernoulli equation:##EQU1##

Referring to FIG. 3, taking the reference point 1 at the second pressuremeasuring means 16' and the second point 2 at the solution source 70 or72, Y₂ -Y₁ =H₁, the height of point 2 with respect to point 1. Further,since the area of the solution source 70 or 72 is much greater than thearea of the solution conduit, 52 or 54, respectively, the velocity atpoint 2 is negligible. Thus

V₂ approximately equals zero. Equation 1 thus simplifies to: ##EQU2##where d is the density of the solution (which is approximately 1 forcardioplegia) and G is the force due to gravity (-9.8 meters per secondsquared) V₁ is the unknown solution velocity at point 1, P₁ is thepressure at point 1 and P₂ is the pressure at point 2. Equation 2 can besolved for V₁ as follows: ##EQU3##

Using Equation No. 3, the instantaneous volume flowing through asolution conduit of radius R can be calculated by multiplying the fluidvelocity by the tube area, πR². Multiplying Equation No. 3 by πR² theinstantaneous solution flow can be calculated as follows: πR² V₁ --theinstantaneous solution volume delivered (flow)

Since the radius of the blood conduit 52 and 54 and 40' (40' is known,as well as the height H₁ (approximately 1 meter) and density of thesolution are fixed and constant. The instantaneous solution flow can becalculated by taking the difference between the measured pressure atpoint 2 and at point 1. It is worth noting that a change in the fluidlevel H₁ or H₂ of the solution sources 70 and 72, respectively, willequally affect the pressure at point 1 and point 2, thereby cancelingthe effects of the drop in fluid level H₁ or H₂. Thus, the instantaneousfluid flow is not affected by the fullness of the solution source.

The computer 80 calculates by discreet time integration the totalsolution volume delivered from the selected solution source, 70 or 72.Further, the computer 80 calculates the blood/solution mixture volume aspreviously described. Using the calculated instantaneous solution volumedelivered and the calculated instantaneous blood/solution mixturedelivered, the computer 80 calculates the blood to solution ratio of theblood/solution mixture by dividing the difference between theblood/solution volume delivered and the instantaneous solution volumedelivered by the instantaneous blood/solution volume delivered.

The VRCD computer 80 of the system invention depicted in FIG. 2 has ameans for displaying the ratio of blood to solution, as well as,optional means for displaying other related and important parameters,such as the coronary sinus pressure measured by the pressure measuringmeans 96 and/or the perfusion pressure in the blood conduit 31 measuredby the pressure measuring means 94. Both pressure measuring means 94 and96 are in-line and adapted to provide an electronic signal correspondingto the measured pressure to the VRCD computer 80.

An alternative embodiment of the system invention 100 replaces thedevice invention 10' with the device invention 10. In that case,rotational sensor 98 and rotational markings 99 are not necessary. Inaddition, pressure measuring means 16' and 18 are not used, rather atleast two of the flow measuring means 12, 14 and 16 are used. In thealternative embodiment of the system invention 100' (not shown), theblood flow measuring means more specifically located in-line with bloodconduit 30 between the output 93 of the split connector and the inlet 22of the Y-connector. Further, the blood/solution mixture flow measuringmeans 14 in-line with blood/solution mixture conduit 34 is morespecifically located between the outlet 23 of the Y-connector and thepump 86.

Although the number, dimensions and volume and pressure outputs of thedevice invention and system invention are not critical, in one operativeembodiment of the device and system invention, the blood andblood/solution mixture conduits are tubular conduits having a 1/4 inchinner diameter and the solution conduits are tubular conduits having a1/16 inch inner diameter. Further, the flow rate of the pump 86 is 50 to500 milliliters per minute, the flow rate of solution from the solutionsources is 5-10 milliliters per minute to 100-250 milliliters perminute. In addition, the pressure of blood conduit 31 deliveringoxygenated blood to the aorta is approximately 100 mmHg. The pressuremeasuring means 16' and 18 are COBE or ABBOTT pressure monitoringtransducers and the flow measuring means I2, 14 and 16 are flow turbinemeters. Other suitable components may be substituted for thesecomponents without substantially departing from the spirit of thisinvention. Further, various modifications and additions may be made andwill be apparent to those skilled in the art. Accordingly, the inventionshould not be limited by the foregoing description, but rather should bedefined only by the following claims.

Having now described the invention in detail in accordance with therequirements of the patent statutes, those skilled in this art will haveno difficulty in making changes and modifications in the individualparts or their relative assembly in order to meet specific requirementsor conditions. Such changes and modifications may be made withoutdeparting from the scope and spirit of the invention, as set forth inthe following claims.

We claim:
 1. A method for mixing blood and solution, for monitoring andfor dispensing the mixture toward a site of perfusion comprising:(a)providing at least one source of blood and at least one source ofsolution; (b) flowing said blood and flowing said solution together toform a flowing mixture having a predetermined ratio corresponding to theflow rates of said blood and said solution; (c) delivering said flowingmixture of blood and solution at a predetermined rate of flow to a siteof perfusion; and (d) monitoring a ratio of blood to solution in saidmixture by a method which comprises:measuring the rate of flow within atleast two of said flowing blood, said flowing solution, and said flowingmixture for calculation of the ratio of blood to solution.
 2. A methodaccording to claim 1 further comprising:(a) converting each flow ratemeasurement into an electronic signal corresponding to the measured rateof flow and which is readable by a computer for calculation of the ratioof blood to solution in said mixture.
 3. A method according to claim 2further comprising:(a) measuring the pressure within said flowingmixture; and, (b) converting said pressure measurement into anelectronic signal corresponding to the measured pressure and which isreadable by a computer.
 4. A method according to claim 2 furthercomprising:(a) diverting a portion of said flowing blood towardperfusion.
 5. A method according to claim 4 further comprising:(a)measuring continuously a pressure of said diverted portion of saidflowing blood; (b) converting said measured pressure to an electronicsignal corresponding to said measured pressure and which signal isreadable by a computer; and, (c) displaying said measured pressure on anelectronic display for continuous monitoring.
 6. A method according toclaim 1 further comprising oxygenating said flowing blood.
 7. A methodfor delivering cardioplegia to a perfusion site comprising:(a) providingat least one source of blood and at least one source of solution; (b)providing a mixing site in communication with said at least one sourceof blood and said at least one source of solution; (c) selectivelycontrolling the rate of flow of said at least one source of blood andsaid at least one source of solution to said mixing site to provide ablood and solution mixture having a predetermined ratio of blood tosolution; (d) delivering said blood and solution mixture to a site ofperfusion; (e) monitoring a ratio of blood to solution within saidmixture by measuring a rate of flow within at least two of said bloodflow, said solution flow, and said mixture flow; and, (f) convertingeach flow rate measurement into an electronic signal corresponding tothe measured rate of flow and which is readable by a computer.
 8. Amethod according to claim 7, further comprising:(a) measuring thepressure within said mixture flow; and, (b) converting said pressuremeasurement into an electronic signal corresponding to the measuredpressure and which is readable by a computer.
 9. A method according toclaim 8 further comprising: oxygenating said flowing blood.
 10. A methodaccording to claim 9 further comprising: diverting a portion of saidflowing blood toward a site of perfusion.
 11. A method according toclaim 10 further comprising:(a) measuring continuously a pressure ofsaid diverted portion of said flowing blood; (b) converting saidmeasured pressure to an electronic signal corresponding to said measuredpressure and which signal is readable by a computer; and, (c) displayingsaid measured pressure on an electronic display for continuousmonitoring.
 12. A method for delivering at a consistent flow rate ablood-additive solution having a predetermined ratio selected within therange of all blood to all solution with respect to a given total volumefor warm or cold cardioplegia treatment of a patient during open heartsurgery comprising:(a) providing at least one source of blood and atleast one source of solution; (b) providing a mixing site; (c)delivering blood from said at least one source of blood at a selectivelyvariable controlled flow rate defining at least one first flow path tosaid mixing site; (d) delivering solution from said at least one sourceof solution at a selectively variable controlled flow rate defining atleast one second flow path to said mixing site; (e) mixing said bloodand said solution together at said mixing site to form a mixture havinga predetermined ratio corresponding to the flow rates of said blood andsaid solution; (f) delivering said mixture of blood and solution at apredetermined rate of flow defining at least one third flow path to asite of perfusion; and (g) monitoring a ratio of blood to solution insaid mixture by a method which comprises:(i) measuring the pressure ofsaid mixture of blood and solution during delivery within said at leastone third flow path to said site of perfusion; (ii) converting saidpressure to an electronic signal corresponding to the pressure measuredand which is readable by a computer; (iii) measuring the rate of flowwithin at least two of said at least one first flow path, said at leastone second flow path, and said at least one third flow path; and (iv)converting each said flow measurement into an electronic signalcorresponding to the measured rate of flow and which is readable by acomputer for calculation of the ratio of blood to solution in saidmixture.
 13. A method according to claim 12 wherein there are twosources of solution.
 14. A method according to claim 12 wherein saidmeasurements are made inline.
 15. A method according to claim 12 furthercomprising displaying said pressure, said rate of flow, and said bloodto additive solution ratio on an electronic display for continuousmonitoring.
 16. A method according to claim 12 further comprising:diverting a portion of blood flow from said first flow path defining atleast one fourth path to said perfusion site.
 17. A method according toclaim 16 further comprising:(a) measuring continuously a pressure ofblood flow in said at least one fourth path means; (b) converting saidmeasured pressure to an electronic signal corresponding to said measuredpressure and which signal is readable by a computer; and, (c) displayingsaid measured pressure on an electronic display for continuousmonitoring.
 18. A method according to claim 12 further comprising:oxygenating said blood in said first flow path.